1. Field of the Invention
The present invention relates to corrosive environment sensors and methods for measuring corrosive environment. More specifically, the present invention relates to a corrosive environment sensor preferable for measuring the corrosive environment inside a space present in a structure and a method for measuring corrosive environment inside a space present in a structure with use of the corrosive environment sensor. The term “corrosive environment” herein refers to an influence of environment exerted on the corrosion of a structure and the like (i.e., corrosiveness of the environment).
2. Description of the Related Art
A structure constituted by combining metallic members may have spaces at portions where the metallic members overlap each other. For example, in the constitution where overlapping portions of metallic members are spot-welded, the metallic members may fail to have a tight contact with each other and thereby a space is generated therein. It has been found out that the inside of such a space is easy to corrode as compared with a portion open to the outside air. The reason thereof is considered as shown below. That is, moisture tends to enter into the inside of such a space and is hardly dried due to capillarity. Accordingly, the humidity inside the space is maintained high as compared with the outside air. To prevent corrosion of metallic members, a method for applying an anticorrosion paint may be used. However, since the anticorrosion paint is hard to sink into the inside of such a space, it may be impossible to sufficiently apply the anticorrosion paint to the inside of the space.
Vehicles such as automobiles also have the structure formed by combining metallic members. For example, the chassis and the body of an automobile are a structure constituted by welding metallic members to each other. When the automobile is driven in the rain and the snow, rainwater and moisture containing snow melting agents may adhere to the structure and enter into a space therein to cause corrosion. Accordingly, it is important for corrosion control design of the automobile structure to understand the corrosive environment of such a space.
As a corrosive environment sensor for measuring the corrosiveness of the environment in which a structure is used, there is known, for example, an ACM (Atmospheric Corrosion Monitor) sensor (hereinafter referred to as “ACM sensor”). The ACM sensor, which has two types of electrodes made of metals having different ionization tendencies, is constituted so that these two types of electrodes are insulated by an insulating material. When water comes into contact with both of these two types of electrodes due to rainfall and dew condensation, a galvanic current flows between the two types of electrodes. The galvanic current has a good correlation with a corrosion rate (i.e., corrosiveness of the environment). Accordingly, the corrosiveness of the environment can be monitored by measuring the galvanic current. In designing constructions such as bridges and residences, the galvanic current is continuously measured with the ACM sensor, and the measurement results are used for calculating life of respective parts of the structure and the like.
However, it is difficult to measure the corrosive environment inside a space present in the structure with use of the ACM sensor. When the electrodes of the ACM sensor come into contact with the structure, electric current may pass between the electrodes and the structure and also the electrodes may short-circuit to each other, which may hinder accurate measurement of the galvanic current. Since the size of the spaces present in the structure is generally small, it is difficult to place the ACM sensor inside minimal spaces without the electrodes coming into contact with the structure.
In the corrosion tests of structures and the like, a combined cyclic corrosion tester may be used. The combined cyclic corrosion tester can reproduce atmospheric corrosion. However, it is difficult to fully reproduce the environment. Moreover, the measurement results have large individual differences and variations.
In order to measure the corrosive environment inside a space between members, a constitution disclosed in Patent Document 1 may be considered for example. A corrosive environment sensor disclosed in Patent Document 1 has space formation members which face a detection section at a specified interval. The space formation members form a space (i.e., a pseudo space) which imitates the actual space formed between members. By placing such a sensor in the vicinity of the portion where members overlap each other in the structure, the corrosive environment of the portion can be measured.
However, the corrosive environment sensor disclosed in Patent Document 1 cannot be placed directly in the space of the portion where the members overlap each other. The portion where the members overlap each other and other portions distanced from that portion are different in factors influencing the corrosive environment and measurement results, such as orientations of the corrosive environment sensor, vibrations of the structure and air currents. It is not possible, therefore, to make the corrosive environment of a pseudo space formed in the corrosive environment sensor completely coincident with the actual corrosive environment of the portion where members overlap each other.    Patent Document 1: Japanese Laid-open Patent Publication No. 2005-134161